WO2013035059A1 - Binders and processes for producing metallic or ceramic moldings in powder injection molding - Google Patents

Abstract

The binders for pulverulent metals, metal alloys or ceramics based on polyacetals, polyethers and polyesters are provided. Additionally, the thermoplastic compositions comprising these binders for the production of metallic or ceramic moldings, the use of these binders and the processes for production of moldings from these binders are provided.

Description

 Binders and process for the production of metallic or ceramic moldings by powder injection molding

description

The present invention relates to binders for powdered metals or pulverulent metal alloys or powdered ceramics, thermoplastic materials containing these binders for the production of metallic or ceramic shaped bodies, their use and processes for the production of molded articles therefrom.

Metallic or ceramic moldings can be produced by injection molding, extrusion or compression of thermoplastic materials which, in addition to metal powders and / or ceramic powders, have an organic binder. These are highly filled organic polymer molding compounds.

After forming the thermoplastic composition into a green part, the organic binder is partially removed in a primary debinder and the resulting debinded green part (= brown part) is further treated. The brown part also contains a binder component that is not removed in the primary debinding. This residual binder is intended to hold the powder particles together in the molded part and is usually expelled by thermal decomposition.

The now completely deboned brown part (= white part) is sintered. Often, but not always, the thermal decomposition of the residual binder is integrated into the sintering cycle.

The first binders for the powder injection molding process were generally based on blends of polyethylene or polypropylene and wax. The green body is first removed from the wax by melting, and the residual binder is burnt out by slow pyrolysis. For melting, the green parts must be stored in a powder bed, because the green strength is practically not given by the melting. Later binder systems for thermal debinding dispensed with the melting, because the elaborate embedding of the green parts in powder and subsequent excavation are far too time-consuming.

Usually, an improved binder system for complete thermal debindering consists of several components, for example polyoxymethylene (POM), polypropylene, waxes and resins as described in DE 199 25 197. These components are successively heated during heating at different temperatures Released moldings, so that the usually lower binder component is still present at least 400 ° C and can be seen as a residual binder. A purely thermal debinding takes 1 to 3 days and is thus extremely slow. A still further improved process is solvent depletion which utilizes binder systems containing binder components of varying solubility. To debind the green part, a binder component is first removed by solvent extraction, after which the remaining, not or very poorly soluble in the solvent residual binder component is again removed by a slow thermal decomposition of the molded part (eg US 4,197.1 18 or EP 501 602). In this case, the melt region of the residual binder is passed through and plastic deformation of the powder molded part is thereby inevitable.

WO 201 1/016718 A1 describes a process for the production of metallic or ceramic shaped bodies, in which a metallic or ceramic sintered powder is mixed with a binder mixture of a polymer, such as e.g. Polyoxymethylene (POM or polyacetal) and a non-polymeric solvent for the polymer (molecular weight <300 g / mol, melting point> RT) a molding composition is formed. The binder preferably contains at least 5% by weight each of the polymer and the non-polymeric solvent. The non-polymeric solvent is evaporated (e.g., at 69 to 130 ° C) or may be dissolved or diluted from the molding compound with another solvent. The remaining polymer is removed by thermal debindering, preferably above 200 ° C. In the examples with a metal powder, POM as a binder component in addition to caprolactam (weight percentages 50:50), the 2-stage thermal debinding with an evaporation at 69 to 130 ° C and a thermal debinding> 240 ° C is disclosed.

A disadvantage of this process is that such binders already evaporate the non-polymeric solvent during mixing with the sintered powder and during processing on the injection molding machine. The low molecular weight component is sweated out on the green part surface and pollutes the injection mold. In addition, the green part strength is significantly reduced. A complete thermal binder removal is also described with polyoxymethylene binders on the example of ceramic powders at temperatures of 160 to 220 ° C. in the presence of air or at 300 to 360 ° C. in the presence of nitrogen (US Pat. No. 5,080,846 A and WO 91/07364 A1). Y. Kankawa (Journal of the Japan Society of Powder Metallurgy 43/7 (1996) 840-845 reports investigations of a thermal debinding in air of a metal powder (SUS316L) with, inter alia, polyacetal as binder component at 300 to 320 ° C. As before carried out, the pure thermal binder removal is very slow and deformation of the moldings occurs very frequently, since the temperatures in the thermal debindering (> 200 ° C) of the metallic molding compounds in a temperature range far above the melt range of polyacetal (160 to 170 ° C. ) lie.

In addition, thermal debinding in an oxygen-containing atmosphere is a problem with the use of metal powders, as opposed to ceramic powders, because the powder surface is generally oxidized in the process and thus compromises the quality and integrity of the sintered article.

Another method for debinding the green part according to the prior art is based on a catalytic debindering by treatment of the green part in a gaseous, acidic atmosphere at elevated temperature. Molding compounds for catalytic debindering come with even less residual binder. In general, the residual binder content is around 10%, the remainder usually being polyacetal.

EP-A 0 413 231 discloses, for example, a process for producing an inorganic sintered molding in which a mixture of a sinterable inorganic powder and polyoxymethylene as a binder is formed into a green body and the binder is then treated by treating the green body in a gaseous, acidic, eg boron trifluoride or HN03, containing atmosphere is removed. Subsequently, the thus treated green body is sintered. Examples of sintered powders are both oxide ceramic powders such as Al ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ and non-oxide ceramic powders such as SiC, Si ₃ N ₄ , and metal powder.

With a binder phase consisting exclusively of POM, however, satisfactory results are not obtained in practice since the brown part strength is completely insufficient and the sintering densities are too low. EP-A 0 444 475 describes binder compositions which are suitable for ceramic molded articles and which, in addition to polyoxymethylene, comprise poly-1,3-dioxolane, poly-1,3-dioxane or poly-1,3-dioxepane as additional soluble polymer or as polymer dispersible in polyoxymethylene aliphatic polyurethanes, aliphatic polyepoxides, poly (C ₂ -C ₆ -alkylene oxides), aliphatic polyamides or polyacrylates or mixtures thereof. EP 0 465 940 A1 and DE 100 19 447 A1 describe thermoplastic molding compositions for the production of metallic moldings which, in addition to a sinterable pulverulent metal or a pulverulent metal alloy, contain a mixture of polyoxymethylene homopolymers or copolymers and a polymer which is immiscible therewith as binder. Suitable additional polymers include polyolefins, in particular polyethylene and polypropylene, as well as polymers of methacrylic acid esters such as PMMA (EP 0 465 940 A1). DE 100 19 447 A1 describes a binder for inorganic material powder for producing metallic and ceramic shaped bodies, said binder is a mixture of polyoxymethylene homo- or copolymers, and a polymer system of polytetrahydrofuran and at least one polymer is selected from C _2- 8-olefins, vinyl aromatic monomers, Vinylestern aliphatic C -s-carboxylic acids, vinyl-Ci _-8- alkyl ethers or Ci-i ₂ -alkyl (meth) acrylates.

WO 2008/006776 A1 describes a binder for inorganic material powder for producing metallic shaped bodies, wherein said binder is a mixture of polyoxymethylene homo- or copolymers, and a polymer system selected from C _2- 8-olefins and poly-1, 3-dioxepane or poly-1, 3- Dioxolane are.

The debindering of the green parts is carried out catalytically using the aforementioned polyoxyethylene binder systems by treating the green part in a gaseous, acidic atmosphere of e.g. Hydrogen halides, formic acid or nitric acid at elevated temperature. The polyoxymethylene homopolymers or copolymers are depolymerized residue-free, followed by a thermal Restent- bindung of the remaining polymer. Here, too, the melt region of the residual binder is passed through and a certain plastic deformation of the powder molded part is thereby unavoidable. The residual binder content after the catalytic removal of the first binder is generally about 10% and is thus lower than after a solvent removal of the first binder, in which the residual binder content is usually from 30 to 70%. A lower residual binder content has the advantage that the plastic deformation of the molded part is usually less pronounced.

A catalytic debinding of moldings with oxalic acid is described in WO 94/25205. The catalytic debinding with oxalic acid, however, is significantly slower in direct comparison with HN0 ₃ and oxalic acid is problematic as a solid in the dosage, so that it has not yet come to industrial use.

US 2008/0075620 A1 describes a catalytic debinding of a molded part obtained by powder injection molding with ozone for the removal of polyethers, polylactides and / or aliphatic polycarbonates as the first binder component. Polyacetal-based polyether components are preferred. The binder phase may also contain a second binder having a higher thermal decomposition temperature than the first binder component which is removed in a subsequent debindering step. The second binder is preferably polystyrene and / or a polyolefin. The proportion of the first component in the binder phase is 20% by weight or more. Mixtures of binders containing polyether or polyacetals and polyester are not described in detail. US 2008/0227906 A1 describes the catalytic debinding of molded parts obtained by powder injection molding with an alkaline gas such as ammonia for the removal of a first binder component, which is preferably based on aliphatic polyesters and / or polyethers. Preference is given to polyesters, in particular polycarbonates and polyhydroxy acids such as polyglycolide and polylactide. The binder phase may include a second binder which has a higher decomposition temperature than the first binder and is removed at a higher temperature in a later debinding step. The second (residual) binder is preferably polystyrene and / or a polyolefin. The proportion of the first binder in the binder phase is 20% by weight or more. Mixtures of binders containing polyethers and polyesters are not described in detail.

Another debinding method for removing polycarbonates with an alkaline gas is described in US 2008/0226489 A1. The residual binder is removed according to the prior art without exception by thermal decomposition. The temperature which is required for the removal of the residual binder from the molded part depends on the polymer selected and on the choice of furnace protection gas, but is usually in the temperature range from 300 to 600 ° C., in particular from 400 to 500 ° C.

The residual debinding may take place separately in a dedicated furnace, especially if the content of residual binder is 30% by weight or more. This has the advantage that the sintering furnace can not be contaminated with pyrolyzed organic substances, which preferably collect at colder places and must be removed regularly by cleaning operations. In addition, a faster heating and thus a shorter cycle time and higher capacity of the sintering plant is possible without pyrolysis of the residual binder in the sintering furnace.

The component producer now has to decide at a very early stage which primary debindering method he wants to use; the system question arises without delay. Thus, there are producers who use the catalytic debinding and remove the residual binder in the sintering furnace. Further, there are producers who prefer solvent predistiltration with subsequent pyrolysis of the residual binder in a burnout furnace prior to final sintering and, in addition, those who, after debinding the solvent, drive off the residual binder in the brown portion in the sintering furnace.

Ready-to-use granules for catalytic debinding are available on the market. Operators of solvent removal are usually backwards integrated and manufacture their granules themselves from purchased powders and binder components; But there are already the first ready-to-use granules for solvent removal on the market.

The choice of system implicitly has the disadvantage that a backwardly integrated operator of a solvent-debonding system does not or only with considerable financial outlay commercially available molding compounds with a large selection of different metal alloys and also ceramics such as the granules intended for catalytic debindering could bring to production.

The backward-integrated producer therefore has the choice between its own, cost-intensive product development and the investment in additional new debindering systems, or it must restrict itself to a smaller product range in an inflexible manner. The task is therefore to develop an improved binder for the production of metallic or ceramic shaped articles , which is universally and flexibly applicable and thus the free choice of the usual methods for binder removal possible. The invention relates to a binder B for producing ceramic or metallic moldings containing

 B-i) from 40 to 95% by weight of at least one polyoxymethylene homopolymer or copolymer;

B ₂ ) from 2 to 60% by weight of at least one polyether selected from poly-1,3-dioxolane, poly-1,3-dioxane, poly-1,3-dioxepan, polytetrahydrofuran, poly-p-dioxanone and their copolymers,

B ₃ ) from 2 to 15% by weight of at least one aliphatic polyester selected from:

wobei R₃ die Gruppierung -(CH)y(CH2)xCH₃, worin x eine ganze Zahl von 0 bis 2 und y eine ganze Zahl von 0 bis 1 ist, und R₄ die Gruppierung (— CH₂— )_z , worin z eine ganze Zahl von 1 bis 5 ist, bedeutet; Polyhydroxyalkanoates containing structural units of the formula (I)

wherein R _{3 is} the moiety - (CH) y (CH 2) x CH ₃ , where x is an integer from 0 to 2 and y is an integer from 0 to 1, and R _{4 is} the moiety (- CH ₂ -) _z , where z is an integer of 1 to 5;

Polycondensates containing structural units of the formula (II)

[- O - R - OC - R ₆ C] (II)

O O

wherein R _{5 is} the moiety (- CH ₂ -) _m , wherein m is an integer from 2 to 4, and R _{6 is} the moiety (- CH ₂ -) _n, wherein m is an integer from 2 to 4;

Polyalkylene carbonates containing structural units of the general formula (III)

[- R ₇ - OC- O-] (Mi)

O wherein R _{7 is} a (dC ₆ ) alkylene radical;

and their stereoisomers and copolymers, the sum of the components B- ₁ ), B ₂ ) and B ₃ ) being 100% by weight.

The proportion of component B-1) is preferably 50 to 90 wt .-%, particularly preferably 50 to 80 wt .-%, based on the total amount of the binder B).

The proportion of component B ₂ ) is preferably 5 to 50 wt .-%, particularly preferably 15 to 45 wt .-%, based on the total amount of the binder B).

The proportion of component B ₃ ) is preferably 3 to 12 wt .-%, more preferably 4 to 10 wt .-%, based on the total amount of the binder B). The polyoxymethylene homopolymers or copolymers (POM) of component B-1) are known as such and are commercially available. The homopolymers are usually prepared by polymerization of formaldehyde or trioxane, preferably in the presence of suitable catalysts. In the context of the invention preferred polyoxymethylene copolymers also contain trioxane and other cyclic or linear formals or other formaldehyde sources as the main monomers. The term main monomers is intended to express that the proportion of these monomers in the total amount of monomers, ie the sum of main and comonomers, is greater than the proportion of comonomers in the total amount of monomers. In general, such POM polymers have at least 50 mol% of repeating units - CH ₂ O- in the main polymer chain. Suitable polyoxymethylene copolymers are described in EP-A 0 446 708 (page 3, line 39 to page 4, line 31). Polyacetals are available on the market, for example, Messrs. BASF under the brand name Ultraform ^® and Fa. Ticona under the brand name Hostaform ^®.

Suitable as component B ₂ ) are polyethers selected from poly-1, 3-dioxolane, poly-1, 3-dioxane, poly-1, 3-dioxepan, polytetrahydrofuran, poly-p-dioxanone and their copolymers. Component B ₂ ) is acid-catalytically at least partially decomposable. The average molecular weights (weight average) of the polyether B ₂ ) are preferably 600 to 100,000 g / mol, in particular 2,000 to 60,000 g / mol.

Among the aforementioned polyethers B ₂ ), poly-1, 3-dioxolane, poly-1, 3-dioxepane and polytetrahydrofuran are preferred. Corresponding products are commercially available or easy to manufacture. Polytetrahydrofuran can be obtained from BASF under the trade name PolyTHF ^®. Poly-p-dioxanone can be obtained from Fa. Evonik under the trade name Resomer ^®.

wobei R₃ die Gruppierung -(CH)y(CH2)xCH₃, worin x eine ganze Zahl von 0 bis 2 und y eine ganze Zahl von 0 bis 1 ist, und R₄ die Gruppierung (— CH₂— )_z , worin z eine ganze Zahl von 1 bis 5 ist, bedeutet, sowie deren Mischungen, deren Stereoisomere und deren Copolymere. The corresponding preparation processes, in particular of polyethers based on 1, 3-dioxepane, 1, 3-dioxane, and 1, 3-dioxolane, are similar to those already described for polyacetal and are known in the art, so that further details are unnecessary here. It is also possible to use mixtures of different polyethers and / or polyethers of different molecular weights. Suitable as component B ₃ ) are in principle all aliphatic polyesters. Particularly suitable are polyhydroxyalkanoates containing structural units of the formula (I)

wherein R _{3 is} the moiety - (CH) y (CH 2) x CH ₃ , where x is an integer from 0 to 2 and y is an integer from 0 to 1, and R _{4 is} the moiety (- CH ₂ -) _z , where z is an integer from 1 to 5, and their mixtures, their stereoisomers and their copolymers.

Examples of these polyhydroxyalkanoates are polyglycolide, polylactide, poly-4-hydroxybutanoate, poly-3-hydroxybutanoate, poly-3-hydroxyvalerate, poly-3-hydroxyhexanoate and polycaprolactone.

Examples of the copolymers are copolyesters of the (L, D) polylactide or copolyester of the aforementioned hydroxybutanoates with 3-hydroxyvalerate or 3-hydroxyhexanoate or copolyesters of polyglycolide, polylactide and polylcaprolactone. Polyglycolide, for example, offered by Fa. Kureda under the brand name Kuredux ^® ; Polylactides in various LD ratios are available from Natureworks under the brand name Ingeo®, various copolymers of glycolide, L- and D-lactide and caprolactone are available from Evonik under the brand name Resomer ^® . Polycaprolactones are available from the company. Perstorp under the trade name CAPA ^®.

Poly-3-hydroxybutyrate-co-4-hydroxybutyrates are known in particular from Metabolix. They are marketed under the trade name Mirel ^®. Poly-3-hydroxybutyrate-co-3-hydroxyhexanoates are known from the company P & G or Kaneka. Poly-3-hydroxybutyrate are sold for example by the company. PHB Industrial under the brand name Biocycle ^® and by the company. Tianan under the name Enmat ^®.

Further suitable aliphatic polyesters are the polycondensates of dicarboxylic acids and diols containing structural units of the formula (II)

[-O- R- O CR ₆ C-] (Ii)

OO wherein R _{5 is} the moiety (- CH ₂ -) _m , where m is an integer from 2 to 4, and R _{6 is} the moiety (- CH ₂ -) _n, where m is an integer from 2 to 4, as well as their mixtures and their copolymers. Examples of these polycondensates are polyethylene and polybutylene malonate, polyethylene and polybutylene succinate, polyethylene and polybutylene glutarate, polyethylene and polybutylene adipate.

Suitable Polybutylensuccinate and polybutylene succinate-co-adipate are examples of playing sold by the company. Showa Denko under the trade name Bionolle ^®. Polyethylensuccinate and polyethylene succinate-co-adipate offered by the company. Nippon Shokubai under the brand name Lunar SE ^®.

Further suitable polyesters are aliphatic polyalkylene carbonates containing structural units of the general formula (III)

[- R ₇ - OC- O-] (Mi)

O wherein R _{7 is} a (dC ₆ ) -alkylene, as well as their mixtures and their copolymers.

Examples of such polyalkylene carbonates are polyethylene and polypropylene carbonate. Suitable polyethylene and polypropylene carbonates are offered for example by the company. Empower Materials Inc. under the brand name QPAC ^®. The aliphatic polyesters B ₃ ) generally have a weight average molecular weight of from 2,000 to 1,000,000, preferably from 20,000 to 100,000.

The polyesters B ₃₎ are preferably selected from poly _(C2-C4) -alkylencarbonat, poly (C ₂ -C ₄₎ -alkylensuccinat, polylactide, polycaprolactone and Polyhydroxybutanoat.

According to a preferred embodiment of the invention, a binder B is provided for producing ceramic or metallic shaped bodies, comprising

 B-i) 50 to 90% by weight of at least one polyoxymethylene homopolymer or copolymer;

B ₂ ) from 5 to 50% by weight of at least one polyether selected from poly-1,3-dioxolane, poly-1,3-dioxepan and polytetrahydrofuran and their copolymers, B ₃ ) 3 to 15 wt .-% of at least one aliphatic polyester selected from: poly (C ₂ -C ₄ ) alkylene carbonate, poly (C ₂ -C ₄ ) alkylene succinate, polylactide, polycaprolactone and polyhydroxybutanoate and their stereoisomers and Copolymers, wherein the sum of the components B- ₁ ), B ₂ ) and B ₃ ) gives 100 wt .-%.

Another object of the invention is a thermoplastic composition for the production of metallic or ceramic moldings, containing

A) 40 to 65% by volume of at least one inorganic sinterable powder A

B) 35 to 60% by volume of a mixture of

 B-i) from 40 to 95% by weight of at least one polyoxymethylene homopolymer or copolymer;

B ₂ ) from 2 to 60% by weight of at least one polyether selected from: polypropylene oxide, poly-1,3-dioxolane, poly-1,3-dioxane, poly-1,3-dioxepane, polytetrahydrofuran, poly- p-dioxanone and its copolymers;

B ₃ ) from 2 to 15% by weight of at least one aliphatic polyester selected from: polyhydroxyalkanoates containing structural units of the formula (I)

wobei R₃ die Gruppierung -(CH)_y(CH₂)_xCH₃, worin x eine ganze Zahl von 0 bis 2 und y eine ganze Zahl von 0 bis 1 ist, und R₄ die Gruppierung (—

where R _{3 is} the grouping - (CH) _y (CH ₂ ) _x CH ₃ , where x is an integer from 0 to 2 and y is an integer from 0 to 1, and R _{4 is} the grouping (-

CH ₂ -) _z , wherein z is an integer of 1 to 5, means;

Polycondensates containing structural units of the formula (II) [-O-R-OC-R ₆ C-] (Ii)

OO wherein R _{5 is} the moiety (- CH ₂ -) _m , wherein m is an integer from 2 to 4, and R _{6 is} the moiety (- CH ₂ -) _n, wherein m is an integer from 2 to 4 ; Polyalkylene carbonates containing structural units of the general formula (II I)

[- R ₇ - OC- O-] (Mi)

O where R _{7 is} a (C ₁ -C ₆ ) -alkylene radical,

 and their stereoisomers and copolymers;

and C) 0 to 5% by volume of a dispersing aid, the sum of components A), B) and C) being 100% by volume.

The inorganic sinterable powder A) can be selected from all known suitable inorganic sinterable powders. Preferably, it is selected from metal powders, metal alloy powders, metal carbonyl powders, ceramic powders, and mixtures thereof.

Examples of metals which may be present in powder form are aluminum, iron, in particular carbonyl iron powder, chromium, cobalt, copper, nickel, silicon, titanium and tungsten. As powdered metal alloys, for example, high or low alloyed steels and metal alloys based on aluminum, iron, titanium, copper, nickel, tungsten or cobalt are mentioned. Both powders of already finished alloys, such as e.g. To name superalloys such as I N713C, GMR 235 and IN 100 and the alloys known from magnet technology with the main components Nd-Fe-B and Sm-Co, as well as to name powder mixtures of the individual alloy components. The metal powders, metal alloy powders and metal carbonyl powders can also be used in a mixture.

Suitable inorganic powders are also oxide ceramic powders such as Al ₂ O ₃ , ZrO ₂ Y ₂ O ₃ but also non-oxide ceramic powders such as SiC, Si ₃ N ₄ , and more complex oxide powders such as NiZnFe ₂ 0 ₄ , and inorganic color pigments such as CoAI ₂ 0 ₄ .

The particle sizes of the abovementioned powders are preferably 0, 1 to 50 μm, more preferably 0.3 to 30 μm. The metal powders, metal alloy powders, metal carbonyl powders and ceramic powders can also be used in a mixture, for example for the production of hard metals such as WC / Co. The optionally present as component C) dispersing agent may be selected from known dispersing aids. Examples are oligomeric polyethylene oxide having an average molecular weight of 200 to 600, stearic acid, stearic acid amide, hydroxystearic acid, fatty alcohols, fatty alcohol sulfonates and block copolymers of ethylene oxide and propylene oxide, and also polyisobutylene. The dispersing aid is particularly preferably used in an amount of from 1 to 5% by volume, based on the components A), B) and C). In addition, the thermoplastic compositions may also contain conventional additives and processing aids which favorably influence the rheological properties of the mixtures during shaping.

The thermoplastic compositions of the invention can be used for the production of metallic or ceramic moldings from the powder A).

The present invention therefore also relates to a process for the production of a metallic or ceramic molding from the thermoplastic composition according to the invention by injection molding, extrusion or compression to form a molded part, followed by removal of the binder and sintering, characterized in that the molded part is used to remove the binder treated according to one of the following variants:

 • Variant 1 with the steps:

1 a) acid-catalyzed debindering of the components B-1 and B ₂ from the molded part and

1 b) subsequent thermal debindering of components B ₃ and optionally C) at 200 to 600 ° C,

or

 • Variant 2 with the steps:

2a) extraction of at least 50% by weight of the binder components B ₂ ) and B ₃ ) and optionally C) from the molded part by a solvent in which the component B-1) is insoluble,

2b) removal of the solvent from the molded part by drying,

2c) subsequent thermal at least partial debindering of the component B1 at 140 to 200 ° C from the molded part in an oxygen-containing atmosphere, and

2d) optionally thermal debindering at 200 to 600 ° C of any remaining amounts of the components B- ₁ ), B ₂ ), B ₃ ) and / or C), or

Variant 3 with the steps: 3a) at least partial extraction of the binder components B ₂ ) and B ₃ ) and optionally C) from the molded part by a solvent in which the component Bi) is insoluble,

 3b) removal of the solvent from the molded part by drying,

3c) subsequent acid-catalyzed at least partial debindering of component Bi) and residual amounts of component B ₂ ) from the molding and

3d) optionally thermal debindering at 200-600 ° C. of the residual amounts of components Bi), B ₂ ), B ₃ ) and / or C) which may still be present. The preparation of the thermoplastic composition of the invention used in the process according to the invention can be carried out in a conventional manner in a kneader or extruder at temperatures of 150 to 200 ° C (see, EP-A 0 413 231). After cooling the mass, it can be granulated. According to a preferred embodiment, the preparation of the thermoplastic mass to be formed by melting the components B) and mixing the components A) and optionally C) take place. For example, component B) can be melted in a twin-screw extruder at temperatures of preferably 150 to 220 ° C., in particular 170 to 200 ° C. Component A) is then metered at temperatures in the same range in the required amount to the melt stream of component B). Advantageously, component A) contains on the surface the dispersant (s) C). However, the preparation of the thermoplastic compositions can also be carried out by melting the components B) and C) in the presence of component A) at temperatures of 150 to 220 ° C. For the molding of the thermoplastic molding composition by injection molding, the usual screw and piston injection molding machines can be used. The molding is generally carried out at temperatures of 175 to 200 ° C and pressures of 3,000 to 20,000 kPa in molds having a temperature of 60 to 140 ° C. The catalytic debinding in step 1 a) and 3c) of the process according to the invention is carried out by acid treatment of the molding preferably at temperatures in the range of 80 to 180 ° C over a period of preferably 0.1 to 24 hours, more preferably 0.5 to 12 hours , The required treatment time depends on the treatment temperature, the concentration and the type of acid in the treatment atmosphere as well as on the size of the shaped body and on the particle size of the powder A. The acid concentration is under the usual conditions about 4 to 5% by volume of the atmospheric gas, which is generally nitrogen.

Suitable acids for the acid-catalyzed debindering in step 1 a) and 3c) of the process according to the invention are, for example, inorganic, at room temperature already gaseous, but at least at the treatment temperature vaporizable acids. Examples are hydrohalic acids and nitric acid. Suitable organic acids are formic acid, acetic acid, oxalic acid or trifluoroacetic acid. Also suitable as acid are BF ₃ or its adducts of organic ethers.

If a conventional carrier gas (inert gas, for example nitrogen) is used for the abovementioned acids, this can be previously passed through the acid and charged with it. The thus loaded carrier gas is then brought to the treatment temperature, which is suitably higher than the loading temperature in order to avoid condensation of the acid. The acids can also be vaporized in the furnace chamber itself and quickly distributed by swirling the furnace atmosphere in the furnace chamber.

The acid is preferably fed to the binder removal furnace via a metering device, evaporated in a shallow dish and uniformly distributed by circulation of the furnace atmosphere.

The acid treatment in step 1 a) and 3c) of the process according to the invention can be carried out in commercially available plants which function according to the principles described in EP-A 0 413 231.

The catalytic binder removal according to step 1 a) and 3c) of the process according to the invention can also be carried out advantageously, especially when using molding compositions containing reactive and / or oxidation-sensitive sinterable powders A, with acids which are solid at room temperature and sublimate at higher temperatures melt and evaporate, including in particular those with a sublimation or melting point between 80 and 200 ° C. Preference is given to oxalic acid, preferably anhydrous oxalic acid, or oxalic acid dihydrate. It is particularly preferred to use a solution of anhydrous oxalic acid in formic acid, acetic acid or mixtures thereof. Furthermore, glyoxylic acid and malonic acid are suitable. Also suitable are benzenesulfonic acid, naphthalenesulfonic acids and maleic acid or mixtures thereof. The abovementioned acids can be used either alone or together with a carrier gas such as air, nitrogen or a noble gas in debinding. In the latter embodiment, the acids used generally reach the debinding temperature initially in the gas phase, act from here on the remaining binder B-ι) and desublimate or solidify after cooling on the walls of the binder removal device. In a subsequent debinding process, they return to the gas phase, ie the acid practically does not leave the device. To facilitate the dosage, it may be appropriate to use the abovementioned acids, which are solid at room temperature and sublimate or melt and evaporate at higher temperatures, as a solution in polar solvents, preferably having boiling points below 200 ° C to use. As such, especially acetone, dioxane, ethanol and acetonitrile are suitable, but especially organic acids such as formic acid and / or acetic acid.

The acid treatment in step 1 a) and 3c) of the process according to the invention is carried out in the variant with acids which are solid at room temperature and sublimate at higher temperatures or melt and evaporate, preferably at temperatures in the range of 100 to 160 ° C.

Preferably, the anhydrous oxalic acid is fed as a solution via a metering the debinding furnace, evaporated and evenly distributed by a circulation of the furnace atmosphere.

The catalytic acid treatment in step 1 a) of the process according to the invention is preferably carried out until the binder components B-1) and B ₂ ) in the molded part are at least 90% by weight, preferably 95% by weight, particularly preferably 98% % By weight are removed.

 The catalytic debindering in step 3c) of the process according to the invention is preferably carried out until the binder component B-1) in the molding is removed to at least 20%, preferably 50%, more preferably 85%, most preferably 95% or more is.

It may be advantageous in step 3 c) to remove the binder component B-1 only partially catalytically, since usually the binder-free components still have to be rearranged for sintering in another furnace and the molding strength then may be insufficient. In such cases, the removal of only 20 to 50% of the binder component B-1) may be more effective; the remaining, stabilizing residue can then be thermally removed in the sintering furnace with an adapted cycle. If this is not necessary, then in step 3 c) a removal of 85 wt .-%, preferably 95 wt .-% or more of the binder component B-ι) should be sought.

In the extraction of the binder components B ₂ ), B ₃ ) and optionally C) from the molding according to step 2a) and 3a) of the inventive method the choice of solvent according to the chemical nature of the aforementioned components. Mixtures of suitable solvents can also be used.

The preferred binder components B ₂ ), B ₃ ) and optionally C) can be dissolved, for example, in aprotic organic solvents such as ethers, esters, amides or ketones, for example tetrahydrofuran, diethyl ether, butyrolactone, dimethylformamide, methyl ethyl ketone or acetone, but also in protic organic solvents such as CrC ₆ -alcohols such as ethanol and isopropanol; Poly-1,3-dioxolane can also be dissolved in water.

If water can be used as a solvent, it is particularly preferred because water provides much easier and environmentally friendlier handling because of its incombustibility. For reactive and / or oxidation-sensitive sintered powder A, when water is used as solvent, this is preferably a conventional corrosion inhibitor, for example modified phosphonates such as amino-tris (methylenephosphonic acid), hydroxyethylamino-di (methylenephosphonic acid) or phosphonobutane-1,2,4-tricarboxylic acid , available eg from Zschimmer & Schwarz.

Extremely reactive sintering powders A are preferably treated with aprotic organic solvents, such as tetrahydrofuran, diethyl ether, butyrolactone, dimethylformamide, methyl ethyl ketone or, preferably, acetone. The treatment of the molding with a solvent according to step 2a) and 3a) of the process according to the invention can be carried out in commercially available plants with closed solvent cycle for the purification of machined, contaminated with lubricants workpieces, described by way of example in DE-A 4337129. Preferably, step 2a) and 3a) at elevated temperature to a maximum of 120 ° C to accelerate the dissolution process, more preferably carried out step 2a) and 3a) at boiling temperature of the solvent under reflux.

The residual binder used for step 2a) and 3a) of the process according to the invention binder component B-ι) - Polyoxymethylenhomo and copolymers (POM) - are resistant to 120 ° C against virtually all common solvents and guarantee even at higher temperatures up to 120 ° C always still a very high strength.

It is of advantage if in step 2a) and 3a) of the process according to the invention a large difference in concentration between the soluble binder components B ₂ ), B ₃ ) and optionally C) in the molding and the solvent during extraction stands. The latter can be achieved by replacing the loaded solvent often with fresh solvent and / or the dissolved extract is quickly carried away, for example by a circulation of the surface of the extraction material.

It may be found and desirable that the binder components B ₂ ) and / or B ₃ ) and optionally C) are only partially soluble in the chosen solvent and are only partially removable in the solvent debinding of step 2a) and 3a). A partial removal of the abovementioned binder components may be advantageous for the strength of the molded parts with regard to handling during the subsequent thermal or catalytic debindering.

Alternatively, the residual binder function desired for conversion into the sintering furnace can also be given by the fact that component B-1) is only incompletely removed in the case of thermal debindering in accordance with step 2c) or in the case of catalytic debindering in step 3c).

Component C) may also be soluble in the same solvents as component (s) B ₂ ) and / or B ₃ ), which is generally advantageous.

The treatment with a solvent according to step 2a) and 3a) of the process of the invention is preferably carried out until the binder components B ₂ ), B ₃ ) and C) at least 50 wt .-%, preferably to 70 wt .-%, more preferably 80 wt .-%, are removed from the molding. This condition is generally reached after 4 to 40 hours. The required treatment time depends on the treatment temperature, the quality of the solvent for the binder components B ₂ ), B ₃ ) and C), the molecular weight of the binder components B ₂ ), B ₃ ) and C), as well as on the size of the molding , After the extraction according to step 2a) and 3a), the green parts, which are now porous and saturated with solvent, still have to be dried. The drying of the molding is preferably carried out in a conventional manner, for example by means of a vacuum drying oven, a heat cabinet or a convection oven, according to step 2b) and 3b) of the method according to the invention.

However, the drying can also be advantageously integrated in step 2c) and 3c) of the method according to the invention. In this case, both the drying and the thermal or catalytic debinding according to step 2c) and 3c) of the component Bi) in the same system, for example in a circulating furnace, are carried out, whereby a reloading of the brown parts is not required. Preferably, the solvent is removed in a separate step 2b) and 3b). The drying temperature is based on the boiling point of the solvent, but is preferably chosen slightly lower in order to avoid the risk of a sudden or too fast drying process with possible negative consequences for the quality of the green part. Usually, the drying according to step 2b) and 3b) of the process according to the invention is completed in 0.5 to 8 h.

The oxidative thermal debindering 2c) of the component B-1) according to the process according to the invention takes place in furnaces in which the moldings are exposed in an oxygen-containing atmosphere to a suitable temperature in the range from 140 to 200 ° C. for a defined period of time. The design and materials of the furnace must ensure that the temperature in the furnace volume is the same everywhere, and good heat transfer to the moldings to be debinded is achieved. In particular, cold spots in the interior of the furnace system are to be avoided in order to prevent the condensation of decomposition products. An oxygen-containing atmosphere is to be understood as meaning a gas mixture of an inert gas such as nitrogen or argon with 1 to 100% by volume of oxygen, with air being preferred. In the case of batch furnaces, internals or circulation elements are known from the prior art, which ensure a uniform distribution and turbulence of the furnace atmosphere, so that all shaped bodies are subjected to the same temperature conditions as possible.

A preferred oven is a conventional convection oven for heat treatments. In particular, at higher loading of the furnace in addition to the gas turbulence sufficient fresh gas supply is necessary (at least tenfold replacement) to sufficiently dilute the decomposition product formaldehyde (<4% by volume) and thus keep the oven in a safe operating condition, eg Air / formaldehyde mixtures are flammable. The oxidative thermal Restentbinderung according to step 2c) of the method according to the invention is preferably carried out until the binder component Bi) at least 20 wt .-%, preferably at 50 wt .-%, particularly preferably at 85 wt .-%, from the molded part is removed. It may be desirable not to thermally remove the entire amount of polyacetal present, since usually the debinded components still have to be relocated to another furnace for sintering, and then the molding strength may become insufficient. In such cases, the removal of only 20 to 50% by weight of the maximum amount of binder component Bi) may be more effective; of the Remaining, stabilizing residue can then be thermally removed in the sintering furnace with an adapted cycle.

The residual binder amount of component B ₃ ) still present after step 1 a) can be expelled in step 1 b), usually integrated into the sintering cycle, by slow heating. The same also applies in steps 2d) and 3d) for optionally remaining amounts of the components B- ₁ ), B ₂ ), B ₃ ), and / or C).

The thermal Restentbinderung or pyrolysis according to because of steps 1 b), 2d) and 3d) can, usually in the sintering furnace, take place under reduced pressure or in a carrier gas to lead out the decomposition products. Usually, for metal powder as the carrier gas, an inert gas such as nitrogen or argon is selected, or else a reducing gas such as e.g. Hydrogen. For ceramic powder, air or, in particular in the case of non-oxide ceramics, an inert gas is usually selected as the carrier gas, or the residual thermal debinding is carried out in a vacuum.

The decomposition range of the residual binder depends on the polymer and the selected atmosphere, but is usually in the temperature range 200 to 600 ° C. In this temperature range, a reduced heating rate of 5 ° C./min, preferably 3 ° C./min, particularly preferably 2 ° C./min, is recommended. At the temperature of the maximum decomposition rate of the polymer, a holding step having a length of 0.25 to 4 hours, preferably 0.5 to 1 hour, may be introduced. For this purpose, in the adjacent temperature ranges below and above this characteristic temperature, a higher heating rate, e.g. 3 to 5 ° C / min, to be selected.

The product thus freed from the binder by the process according to the invention can be converted in the usual way by sintering at temperatures above 600 ° C. to 2000 ° C. into a metallic or ceramic shaped body. The sintering may optionally take place at an accelerated heating rate of 5 to 10 ° C / min in the temperature range of 200 to 600 ° C, if there is no residual binder more.

The molding compositions of the invention are universally applicable and are suitable for various methods for the production of moldings. The shaped bodies according to the invention can be used as components.

The invention is explained in more detail below with reference to examples: In the following examples, test compounds were homogenized in a cone mixer and homogenized and granulated in a laboratory extruder heated to 190 ° C.

 The test mass with ceramic powder according to Example 9 was prepared in a heated to 180 ° C sigma kneader with a kneading time of 2 h.

example 1

 The molding compound 1 had the following composition:

 56.75% by volume of a mixture of 98% by weight of carbonyl iron powder and 2% by weight of carbonyl nickel powder (FN 2)

 43.25% by volume of binder containing

 + 62 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane

 + 29% by weight polydioxolane (PDL) with a molecular weight of 28,000,

 + 9 wt% polylactide (PLA) with a molecular weight of 120,000

In the molding compound 1, the proportion by weight of the binder components B1, B2, and B3 is thus as follows:

B1 7.26% by weight

B2 3.39% by weight

B3 1, 1 1% by weight

Example 2

 The molding compound 2 had the following composition:

 56.75% by volume of a mixture of 98% by weight of carbonyl iron powder and 2% by weight of carbonyl nickel powder (FN 2)

 43.25% by volume of binder containing

 + 48 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane

 + 43% by weight polydioxolane (PDL) with a molecular weight of 28,000,

 + 9 wt% polylactide (PLA) with a molecular weight of 120,000

In the molding compound 2, the proportion by weight of the binder components B1, B2, and B3 is thus as follows:

B1 5.62% by weight

B2 5.05% by weight

B3 1, 08% by weight

Example 3

The molding compound 3 had the following composition: 56.75% by volume of a mixture of 98% by weight of carbonyl iron powder and 2% by weight of carbonyl nickel powder (FN 2)

 43.25% by volume of binder containing

 + 86 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane

 + 3% by weight polytetrahydrofuran (PTHF) with molecular weight 2000,

 + 1 1 wt% polybutylene succinate (PBS) having a molecular weight of 109,000

In the molding compound 3, the proportion by weight of the binder components B1, B2, and B3 is thus as follows:

B1 10.17% by weight

B2 0.36% by weight

B3 1, 32% by weight

Example 4

The molding compound 4 had the following composition:

 56.75% by volume of a mixture of 98% by weight of carbonyl iron powder and 2% by weight of carbonyl nickel powder (FN 2)

 43.25% by volume of binder containing

 + 67 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane

 + 24% by weight polydioxolane (PDL) with a molecular weight of 12,500,

 + 9 wt% polybutylene succinate (PBS) having a molecular weight of 109,000

In the molding compound 4, the proportion by weight of the binder components B1, B2, and B3 is thus as follows:

B1 7.90% by weight

B2 2.81% by weight

B3 1, 13% by weight

Example 5

The molding compound 5 had the following composition:

 56.75% by volume of a mixture of 98% by weight of carbonyl iron powder and 2% by weight of carbonyl nickel powder (FN 2)

 43.25% by volume of binder containing

 + 68 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane

 + 24% by weight polydioxolane (PDL) with a molecular weight of 28,000,

 + 8 wt% polycaprolactone (PCL) with a molecular weight of 23,600

In the molding compound 5, the proportion by weight of the binder components B1, B2, and B3 is thus as follows:

B1 7.91% by weight B2 2.81% by weight

B3 0.99% by weight

Example 6

The molding compound 6 had the following composition:

 56.75% by volume of a mixture of 98% by weight of carbonyl iron powder and 2% by weight of carbonyl nickel powder (FN 2)

 43.25% by volume of binder containing

 + 79 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane

 + 16% by weight of polydioxepane (PDP) with a molecular weight of 33,000,

 + 5 wt% poly-3-hydroxybutyrate-co-3-hydroxyvalerate, (PHBV), having a molecular weight of 840,000

In the molding compound 6, the proportion by weight of the binder components B1, B2, and B3 is thus as follows:

 B1 9.08% by weight

B2 1, 90% by weight

B3 0.55% by weight Example 7

 The molding compound 7 had the following composition:

 56.75% by volume of a mixture of 98% by weight of carbonyl iron powder and 2% by weight

Carbonylnickel powder (FN2)

 43.25% by volume of binder containing

 + 69 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane

 + 29% by weight polydioxolane (PDL) with a molecular weight of 28,000,

 + 2.4% by weight of polypropylene carbonate (PPC) having a molecular weight of 89,000

In the molding compound 7, the proportion by weight of the binder components B1, B2, and B3 is thus as follows:

 B1 8.14% by weight

B2 3.41% by weight

B3 0.29 wt% Example 8

 The molding compound 8 had the following composition:

 64% by volume of a metal powder of composition 316L (DIN 1.4404) with an average particle size of 10 μm

 36 vol% binder containing

+ 62 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane + 29% by weight polydioxolane (PDL) with a molecular weight of 28,000,

 + 9 wt% polylactide (PLA) with a molecular weight of 120,000

In the molding compound 8 is thus the weight fraction of the binder components B1, B2, and

B3 as follows:

 B1 5.31% by weight

 B2 2.43% by weight

 B3 0.80 wt% Example 9

 The molding compound 9 had the following composition:

47% by volume of a ceramic powder having the composition ZrO ₂ - 5% by weight of Y ₂ O ₃ (TZP) with an average particle size of 0.3 μm

 51 vol% binder containing

 + 79 wt .-% polyoxymethylene with 2 mol% 1, 3-dioxepane

 + 19% by weight polydioxepan (PDP) with a molecular weight of 12,500,

 + 2% by weight of polybutylene succinate (PBS) having a molecular weight of 109,000

 2% by volume of dispersing agent C, an ethoxylated fatty alcohol with a molar mass of 600 In the molding compound 9, the proportion by weight of the binder components B1, B2, and B3 is thus as follows:

B1 13.56% by weight

B2 3.30% by weight

B3 0.41% by weight

C 1, 70% by weight

Spritzqießversuche on real components

 The examination of the general suitability of the test masses was carried out with a complex and heavy component, a hinge of complex geometry injection-molded with two band hinges at positions 1 (FIG. 1: top view, bottom view of the component).

The length of the component was 100 mm, the weight of the sintered part obtained was about 34 g for examples 1 to 7, about 40 g for example 8 and about 26 g for example 9.

This ensures that the results of the tests are also relevant to practice because the weight of this component makes above-average demands on the strength after debindering. Investigation of the processing on the injection molding machine

 The test masses were melted in the cylinder of the injection molding machine at 190 ° C, the injection mold was heated to 135 ° C. In general, the required injection pressure was approx. 1500 - 1800 bar, a normal value for POM-based injection molding compounds.

The test masses differed in the cooling time required before demolding. The test masses with a higher content of component B ₂ ) (30% and higher) were somewhat softer and required a longer cooling time in order to be able to demold the green part intact; the green parts also showed some streaks on the surface.

For all test masses, processing was possible in the usual way. Only the test mass 2 with a high PDL content. could only be processed with a pressure of 600 bar. In addition, the melt temperature and the mold temperature had to be lowered by about 10 ° C.

Examination of debinding and sintering Variant 1 - Catalic and thermal debinding

The primary catalytic acid debinding was carried out with the components of Examples 1 to 9 in a 50 L laboratory oven at 110 ° C. It was purged for inerting with 500 L / h of nitrogen, after 1 h 30 ml / h HN0 _{3 were} dosed into it and further purged with 500 l / h of nitrogen oven and evaporated.

Thus, the green parts of Examples 1 to 9 were subjected to catalytic debindering. After 6 h of debindering time, the proportion of catalytically decomposable binder components (Bi + B ₂ ) of all components was at least 90% removed (Table 1).

Table 1 Effect of acid-catalytic debindering

The obtained after debindering powder moldings of Examples 1 to 7 were thermally debindered in a 30-L sintered furnace with molybdenum cladding and Molybdänsinterelementen under nitrogen, first at temperatures from RT to 600 ° C and then at higher temperatures up to 1280 ° C under nitrogen of quality 4.8 sintered.

The sintering curve was as follows:

 Room temperature up to 600 ° C at 5 ° C / min

 Holding time at 600 ° C: 1 h

 600 ° C to 1280 ° C at 5 ° C / min.

 Holding time at 1280 ° C: 1 h

 Cool at 5 ° C / min to 1000 ° C

 Oven off, natural refrigeration.

With this sintering program, it was possible for almost all molding compositions according to Examples 1 to 7, intact sintered parts with a good sintering density of at least 7.59 g / cm ³ to achieve (see Table x).

Only the molding composition according to Example 4 reached only a sintered density of 7.42 g / cm ³ under these conditions. A good density of 7.61 g / cm ³ could be achieved with this molding compound at a reduced heating rate of 3 ° C / min in the range RT to 600 ° C; this finding justifies the preferred lower limit of 90% for the catalytic debindering of POM according to variant 1, because the lower heating rate adversely affects the capacity of the sintering furnace and thus the economic efficiency of the process. The molded article according to Example 8 obtained by the process according to the invention was sintered in the same sintering furnace under quality 4.8 hydrogen. The sintering curve was as follows:

 Room temperature up to 600 ° C at 5 ° C / min

- Holding time at 600 ° C: 1 h

 600 ° C to 1380 ° C at 5 ° C / min

 Holding time at 1380 ° C: 1 h

 Cool at 5 ° C / min to 1000 ° C

 Oven off, natural refrigeration.

Again, it was possible to obtain intact sintered parts. The sintered parts achieved a good sintering density of 7.89 g / cm ³ .

The powder molding of Example 9 obtained after catalytic debinding was sintered in air in a commercial ceramic sintering furnace with the following schedule.

 Room temperature up to 270 ° C at 3 ° C / min

 Holding time at 270 ° C: 1 h

 270 ° C to 1500 ° C at 3 ° C / min

- Holding time at 1500 ° C: 1 h

 Cool at 5 ° C / min to 1000 ° C

 Oven off, natural refrigeration

The obtained sintered parts were intact, defect-free and had a good sintered density of 6.05 g / cm ³ .

Table 2 Sintered density of the thermally debindered and sintered moldings

Example sintered density g / cm ^J

 1) FN2 - 29 PDL - 9 PLA 7.63

 2) FN2 - 43 PDL - 9 PLA 7.62

 3) FN2 - 3 PTHF - 11 PBS 7.59

 4) FN2 - 24 PDL - 9 PBS 7.42 (7.61)

 5) FN2 - 24 PDL - 8 PCL 7,59

 6) FN2 - 16 PDP - 5 PHBV 7.60

 7) FN2 - 29 PDL - 2.4 PPC 7.63

 8) 316L - 29 PDL - 9 PLA 7,89

9) TZP - 19 PDP - 2 PBS 6.05 Variant 2 - solvent removal + thermal debinding

 The green parts produced from the test masses were pretreated in a solvent, after which the molded part was dried, thermally restentbindert and sintered.

For the solvent debinder, the green parts were treated in a stirred three-necked flask in boiling solvent (acetone, ethanol, water and chloroform were used) under reflux for 24 h. Only Example 8 had to be treated for 48 hours for debinding in water.

The weight loss was determined after drying for 4 h in a convection oven at the boiling point of the solvent.

Table 3 Effect of solvent removal

^* in% of (B ₂ + B ₃ + C)

The green parts of Examples 1 and 8 show that the choice of solvent (acetone, ethanol or water) decides whether and how much of the binder component B ₃ ) is dissolved.

Example 8 shows a solvent removal of poly-1,3-dioxolane as component B ₂ ) with water. The debindering is only half as fast, but otherwise works flawlessly.

Subsequently, the moldings were thermally de-bindered in air. The thermal debinding was carried out in a gas-tight, air-circulated 50 L air oven with 500 L / h of air. The moldings were heated for 12 h in the 165 ° C on heated oven treated. Thereafter, the moldings were removed and the weight loss was determined (Table 4).

Effect of thermal debinding

^** cracks in the molding

The determined weight loss is in most of the examples close to or slightly above the content of binder component B-1) and demonstrates the effectiveness of the method according to the invention. The additional weight loss has its origin in the residue of binder component B ₂ ) not dissolved in the preceding solvent debinder, which is then degraded during thermal debindering. The components of Examples 4 and 6 showed cracks or delaminations; the weight loss remains well below the expected from the content of component B-ι) value. Here, the loss of binder components B ₂ ) and B ₃ ) in step 2a) was less than the preferred 70%.

With a much slower step program, however, these moldings were thermally unbuteable intact. The following program was used for this:

Stage Ti T ₂ Heating rate Ve at T ₂

 [° C] [° C] [° C / h] [h]

0 RT 130 300 1

 1 130 140 10 6

 2 140 150 10 16

 3 150 160 10 1

 4 160 170 10 1

 5 170 170 5

With this heating program it was possible to obtain intact unbound moldings; the weight loss is reported in brackets in Table 3. It is thus possible to work with at least 50% weight loss of binder components B ₂ ) and B ₃ ) in step 2a).

However, the slower program reduces the economy and often has to be fine-tuned and adjusted in practice, depending on the geometry and wall thickness of the molded part and is therefore more expensive.

The molded parts treated according to the two-stage debinding method of variant 2 were sintered as described in variant 1. The sintered parts, including those from Examples 4 and 6 with the slower heating program, were intact and error-free (Table 5).

Table 5 sintered densities of the sintered moldings

Example solvent sintered density

g / cm ³

 1) FN2 - 29 PDL - 9 PLA acetone 7.63

 Ethanol 7.61

 2) FN2 - 43 PDL - 9 PLA acetone 7.62

 3) FN2 - 3 PTHF - 11 PBS chloroform 7.63

 4) FN2 - 24 PDL - 9 PBS acetone (7.60)

 5) FN2 - 24 PDL - 8 PCL acetone 7.59

 6) FN2 - 16 PDP - 5 PHBV acetone (7.59)

 7) FN2 - 29 PDL - 2.4 PPC acetone 7.61

 8) 316L - 29 PDL - 9 PLA acetone 7,94

 Water 48 h 7,93

9) TZP - 19 PDP - 2 PBS acetone 6.06 Variant 3 - solvent debinding + catalytic debinding

 The solvent debinding was carried out with the molding compositions of Examples 1 to 9 in the same solvents as in Variant 2.

Subsequently, the moldings were dried at 60 ° C. The drying and catalytic debinding were carried out in a gas-tight, circulated with 500 L / h of nitrogen 50 L furnace with circulation. The catalytic debinding was carried out as in Variant 1. Thereafter, the moldings prediluted in the solvent were dried in a convection oven at the boiling point of the solvent and subjected to catalytic debindering as described for variant 1. The weight loss was determined with respect to the weight of the untreated molding (Table 6). Table 6 Effect of solvent and catalytic debinding

The determined weight loss after catalytic debindering is in all examples again usually just below or slightly above the content of binder component B-1) and demonstrates the effectiveness of this variant of the method according to the invention.

The additional weight loss also finds its origin in the residual of binder component B ₂ ) which is not dissolved in the preceding solvent debindering, which is also degraded during the catalytic debindering. All molded parts obtained by the two-stage debinding method of variant 3 were sintered as described in variant 1. The sintered parts were intact and free of defects (Table 7). Table 7 sintered densities of the treated according to variant 3 molded parts

Example solvent sintered density

g / cm ³

 1) FN2 - 29 PDL - 9 PLA acetone 7.62

 Ethanol, 7.62

 2) FN2 - 43 PDL - 9 PLA acetone 7.62

 3) FN2 - 3 PTHF - 11 PBS chloroform 7.62

 4) FN2 - 24 PDL - 9 PBS acetone 7.61

 5) FN2 - 24 PDL - 8 PCL acetone 7.60

 6) FN2 - 16 PDP - 5 PHBV acetone 7.60

 7) FN2 - 29 PDL - 2.4 PPC acetone 7.62

 8) 316L - 29 PDL - 9 PLA acetone 7,91

 Water 48 h 7.90

 9) TZP - 19 PDP - 2 PBS acetone 6.06

Claims

claims 1 . Binder B for the production of ceramic or metallic moldings containing  B-i) from 40 to 95% by weight of at least one polyoxymethylene homopolymer or copolymer, B ₂ ) from 2 to 60% by weight of at least one polyether selected from poly-1,3-dioxolane, poly-1,3-dioxane, poly-1,3-dioxepan, polytetrahydrofuran, poly-p-dioxanone and their copolymers, B ₃ ) from 2 to 15% by weight of at least one aliphatic polyester selected from: Polyhydroxyalkanoates containing structural units of the formula (I)

wherein R _{3 is} the moiety - (CH) _y (CH ₂ ) _x CH ₃ , wherein x is an integer from 0 to 2 and y is an integer from 0 to 1, and R _{4 is} the moiety (- CH ₂ -) _z wherein z is an integer of 1 to 5; Polycondensates containing structural units of the formula (II)

wherein R _{5 is} the moiety (- CH ₂ -) _m , wherein m is an integer from 2 to 4, and R _{6 is} the moiety (- CH ₂ -) _n, wherein m is an integer from 2 to 4; Polyalkylene carbonates containing structural units of the general formula (III) [- R ₇ - OC- O-] (Mi) O wherein R _{7 is} a (Ci - C ₆ ) -Alkylenrest; and their stereoisomers and copolymers, the sum of components B- ₁ ), B ₂ ) and B ₃ ) being 100% by weight. 2. Binder B according to claim 1, containing  B-i) 50 to 90 wt .-% of at least one Polyoxymethylenhomo- or -copolymerisats; B ₂ ) from 5 to 50% by weight of at least one polyether selected from poly-1,3-dioxolane, poly-1,3-dioxepan and polytetrahydrofuran and copolymers thereof, B ₃ ) from 3 to 12% by weight of at least one aliphatic polyester selected from: Poly (C ₂ -C ₄ ) -alkylene carbonate, poly (C ₂ -C ₄ ) -alkylenesuccinate, polylactide, polycaprolactone and polyhydroxybutanoate and their stereoisomers and copolymers, the sum of components Bi), B ₂ ) and B ₃ ) being 100% by weight. 3. Thermoplastic material for the production of metallic or ceramic moldings, containing  A) 40 to 65 vol .-% of at least one inorganic sinterable powder A B) 35 to 60 vol .-% of a mixture of  B-i) from 40 to 95% by weight of at least one polyoxymethylene homopolymer or copolymer; B ₂ ) 2 to 60 wt .-% of at least one polyether selected from: poly-1, 3-dioxolane, poly-1, 3-dioxane, poly-1, 3-dioxepan, polytetrahydrofuran, poly-p-dioxanone and their copolymers; B ₃ ) from 2 to 15% by weight of at least one aliphatic polyester selected from: Polyhydroxyalkanoates containing structural units of the formula (I)

wherein R _{3 is} the moiety - (CH) _y (CH ₂ ) _x CH ₃ , wherein x is an integer from 0 to 2 and y is an integer from 0 to 1, and R _{4 is} the moiety (- CH ₂ -) _z wherein z is an integer of 1 to 5; Polycondensates containing structural units of the formula (II) [-O- R- OC -R ₆ C-] (Ii) OO wherein R _{5 is} the moiety (- CH ₂ -) _m , wherein m is an integer from 2 to 4, and R _{6 is} the moiety (- CH ₂ -) _n, wherein m is an integer from 2 to 4 ; Polyalkylene carbonates containing structural units of the general formula (III) [- R ₇ - OC- O-] (Mi) O where R _{7 is} a (C ₁ -C ₆ ) -alkylene radical,  and their stereoisomers and copolymers;  and C) 0 to 5 vol .-% of a dispersing aid, wherein the sum of components A), B) and C) 100 wt .-% results. 4. Thermoplastic composition according to claim 3, characterized in that the inorganic sinterable powder A is selected from metal powders, metal alloy powders, metal carbonyl powders, ceramic powders and mixtures thereof. 5. Use of the thermoplastic compositions according to claim 3 or 4 for the production of metallic or ceramic moldings. 6. Metallic or ceramic molding, prepared from thermoplastic molding compositions according to claim 3 or 4. 7. A process for the production of metallic or ceramic moldings from a thermoplastic composition according to claim 3 or 4 by injection molding, extrusion or compression to a molding, subsequent removal of the binder and sintering, characterized in that for removing the binder, the molding according to one of the following variants: • Variant 1 with the steps: 1 a) acid-catalyzed debindering of the components B-1 and B ₂ from the molded part and 1 b) subsequent thermal debindering of the components B ₃ and, if appropriate, C at 200-600 ° C., or  • Variant 2 with the steps: 2a) extraction of at least 50% by weight of the binder components B ₂ ) and B ₃ ) and optionally C) from the molded part by a solvent in which the component B-1) is insoluble,  2b) removal of the solvent from the molded part by drying, 2c) subsequent thermal at least partial debindering of component B-i) at 140-200 ° C from the molded part in an oxygen-containing atmosphere, and 2d) optionally thermal debindering at 200-600 ° C. of the residual amounts of components Bi), B ₂ ), B ₃ ) and / or C) which may still be present, or  • Variant 3 with the steps: 3a) at least partial extraction of the binder components B ₂ ) and B ₃ ) and optionally C) from the molded part by a solvent in which the component Bi) is insoluble, 3b) removal of the solvent from the molded part by drying, 3c) subsequent acid-catalyzed at least partial debindering of component Bi) and residual amounts of component B ₂ ) from the molding and 3d) optionally thermal debindering at 200-600 ° C. of the residual amounts of components Bi), B ₂ ), B ₃ ) and / or C) which may still be present.